1. Field of the Invention
The present invention relates to waste treatment devices and, in particular, to a method of recovering a disposal trench with a biomat slime, and a method of operating a waste treatment vessel.
2. Description of the Related Art
In a conventional non-municipal waste system, waste material flows into a septic tank. The septic tank is a separator that separates the waste material into three distinct regions. The regions include a lower layer that is formed from solids settling out of the waste material, and an upper layer that is formed from lighter waste material floating to the top of the septic tank.
The regions of the septic tank also include a middle liquid layer, known as effluent, which is ideally free of solids and floating material. Significant components of the effluent include ammonia and dissolved organic compounds. Following the separation, the effluent flows out to a disposal trench that allows the effluent to seep into the soil.
The septic tank is a sealed vessel and, as a result of having no oxygen, is colonized by anaerobic bacteria. The anaerobic bacteria, however, are inefficient role in consuming or breaking down the waste material. However, as a result of the anaerobic bacteria being present in the septic tank, the effluent flowing out to the disposal field also includes anaerobic bacteria.
Once in the disposal trench, naturally occurring strict aerobic bacteria in the soil consume and break down the carbon-based material in the effluent stream. In addition, one type of strict aerobic bacteria converts the ammonia in the effluent stream into nitrites (NO2), while another type of strict aerobic bacteria converts the nitrites into nitrates (NO3).
One problem with a conventional septic tank is that, over time, the anaerobic bacteria in the effluent stream seal the bottom of, and then fill up, the disposal trench. As the anaerobic bacteria flow out into the disposal trench, the anaerobic bacteria move from the anaerobic (no oxygen) condition of the septic tank to the aerobic (oxygen available) condition present in the soil.
To insulate itself from the aerobic conditions in the soil (anaerobic bacteria die in the presence of oxygen), the anaerobic bacteria form a slime, known as a biomat. The biomat prevents the effluent from seeping into the soil, and eventually fills up the disposal trench, thereby preventing any further effluent from flowing into the disposal trench. When this happens, the septic system fails.
Another problem with a conventional septic tank is that the bacteria in the soil convert the ammonia in the effluent into nitrates. Nitrates are stable compounds and can leach into the aquifer and contaminate drinking water wells as well as pollute fresh and marine aquatic environments. Thus, there is a need for a method of operating a septic tank that prevents anaerobic bacteria in the effluent from forming a slime in the disposal trench, and prevents nitrates from being formed in the soil.
Municipal waste treatment facilities differ from non-municipal waste systems in that municipal waste systems typically treat and then discharge the effluent to a surface water system such as a river or lake. One of the treatments that must take place is the removal of ammonia from the effluent stream. Ammonia is toxic to fish and other aquatic organisms.
In many facilities, the effluent is aerated which, in turn, allows two types of strict aerobic bacteria to grow. The two types of strict aerobic bacteria that result from the aeration, like the strict aerobic bacteria in the soil, convert the ammonia first to nitrites, and then to nitrates. The nitrates, which are less toxic to fish than ammonia, are then discharged to the water system with the treated wastewater.
Nitrates discharged in wastewater, however, have a significant environmental impact. Nitrates are an important plant nutrient that, especially in near-shore marine environments, stimulates blooms of a wide range of noxious algae and dinoflagellates such as Alexandrium and Pfisteria, both of which are highly toxic.
A number of biological methods exist for de-nitrifying wastewater where the nitrogen in the ammonia is eventually converted to nitrogen gas or other gaseous nitric oxides. The resulting nitrogen gas, which makes up over 70% of the Earth""s atmosphere, is entirely benign.
The most common method of de-nitrification used in municipal wastewater treatment systems is to first oxidize the ammonia to nitrite (NO2) with bacteria such as Nitrosomonas or Nitrosococcus. The nitrite is then oxidized to nitrate (NO3) using bacteria such as Nitrobacter. If this nitrate is then circulated to an anaerobic (no oxygen) zone in the presence of a sufficient amount of carbon, facultative anaerobic bacteria in the anaerobic zone can utilize the nitrate as an oxygen source to form CO2. In the process, the nitrate is first converted to nitrite, and then to nitrogen gas.
One problem with this approach, however, is that it takes far more energy to convert the ammonia to nitrites, and the nitrites to nitrates than it does to circulate and aerate the carbonaceous organic material to oxidize the carbon and form CO2. When aeration is used to convert the ammonia to nitrites, and the nitrites to nitrates, it takes almost five times the amount of aeration to oxidize ammonia to nitrate as it does to oxidize the carbonaceous organic material to form CO2.
Thus, there is also a need for a municipal waste treatment system that removes nitrogen, including ammonia, nitrites, and nitrates, from the wastewater in a more energy efficient manner.
The present invention provides a method of recovering a soil-based disposal trench that has a biomat slime. The method includes the step of adding facultative anaerobic bacteria to an effluent that flows into the disposal trench. The step of adding facultative anaerobic bacteria to an effluent that flows into the disposal trench includes the steps of circulating the waste material in the treatment vessel, and adding facultative anaerobic bacteria to the treatment vessel. The circulation of the waste material causes the effluent that flows into the disposal trench to include facultative anaerobic bacteria.
The present invention also provides a method for operating a waste treatment vessel that holds waste material. The method includes the step of aerating and circulating the waste material in the treatment vessel until a predetermined number of a first type of strict aerobe and a second type of strict aerobe have colonized the treatment vessel. The first type of strict aerobe converting ammonia to nitrites, while the second type of strict aerobe converts nitrites to nitrates.
The method also includes the steps of adding facultative anaerobic bacteria to the treatment vessel. The facultative anaerobic bacteria added to the effluent substantially replace the second strict aerobic bacteria in the treatment vessel that convert nitrites to nitrates by exclusion and prevent them from recolonizing.
The present invention also includes a waste treatment device. The waste treatment device in accordance with the present invention includes an air diffuser that has a bubble output side that provides bubbles of air evenly across a diameter of a column that extends away from the bubble output side.
The waste treatment device also includes a bacteria container that is positioned within the column a predetermined distance away from the bubble output side of the diffuser. Bubbles passing by the bacteria container cause a bacteria to be released into a flow. The waste treatment device additionally includes a structure that contacts the bacteria container to position the bacteria container in the column.
The waste treatment device can also include a bacterial host material that is positioned within the column a predetermined distance away from the bubble output side of the diffuser. The bacterial host material is non-corrosive. The bacteria in the flow from the bacteria container grow on the bacterial host material.
The present invention also includes a method of operating a waste treatment device. The method includes the step of placing a facultative anaerobic culture in the bacteria container. The method also includes the step of forcing air into the diffuser so that air bubbles rise up through the column. Bubbles passing by the bacteria container cause bacteria from the culture to be released into a flow. The method further includes the step of directing the flow into a soil treatment system. In addition, the method of the present invention can also include the step of forming a nitrifying bacteria on the bacterial host material prior to placing the facultative anaerobic culture in the bacteria container.
A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description and accompanying drawings that set forth an illustrative embodiment in which the principles of the invention are utilized.